1. Field of the Invention
The present invention relates to a jitter measuring apparatus for measuring jitter of a signal to be measured and a testing apparatus for testing an electronic device. In addition, the present invention relates to the following Japanese patent application. The present invention claims the benefit of, and priority to, Japanese patent application No. 2002-288799 filed on Oct. 1, 2002, the entire contents of which are incorporated herein by reference for all purposes.
2. Description of Related Art
Recently, a requirement of high operation speed and low cost of a semiconductor device is prominent. Accordingly, it is required to measure jitter of an output signal of the semiconductor device precisely. For example, in case of transferring data between semiconductor devices, it is required to measure jitter of a clock for transferring the data (DQS) precisely. In case jitter is generated in the DQS, the semiconductor device cannot transfer the data accurately.
For example, in case of storing the data in the semiconductor device according to an edge of the clock, it is required to stabilize the data given to the semiconductor device to be a desired value before the clock edge. In this case, sometimes the storage of the data cannot be correctly performed if jitter is generated in the clock. Thus, measurement of jitter of the clock and the like is conducted as a testing of the semiconductor device.
Conventionally, in case of measuring jitter of a signal to be measured, the signal to be measured is output many times, strobe signals of which phases are different little by little are generated for each signal to be measured, and the signal to be measured is scanned by the strobe signals of different phases to detect an edge of the signal to be measured. By repeating the procedures and detecting the edge of the signal to be measured many times, the jitter of the signal to be measured is measured.
However, since the conventional jitter measuring method detects the edge of the signal to be measured one time, the signal to be measured is output many times. In order to measure the jitter of the signal to be measured, it is required to detect the edge of the signal to be measured many times. Thus, the conventional measuring method takes much time for measurement. Further, since one edge is detected from signal to be measured output many times, it is impossible to measure the jitter of the signal to be measured precisely.
Accordingly, it is an object of the present invention to provide a jitter measuring apparatus and a testing apparatus, which are capable of over coming the above drawbacks accompanying the conventional art. The above object can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.